We intend to determine the extent to which DNA of chromosomes binds alkyl and aryl mercury in living cells. Also, we wish to obtain information on the molecular level concerning the nature of the complexes. The method to be used is a spectroscopic one, optical detection of magnetic resonance (ODMR) by means of which magnetic resonance transitions in photoexcited triplet states are detected optically. A heavy atom effect caused by mercury binding to an aromatic chromophore such as a heterocyclic base of DNA makes the resulting triplet state a highly radiative trap which is especially sensitive to ODMR. The ODMR method thus selects the mercury-perturbed chromophore which then can be identified by the magnetic resonance frequencies and other properties of the phosphorescent state. Selectivity by the heavy atom effect is especially good in DNA which normally is not highly luminescent. As a major system for study, we intend to use Allium cepa, for which cytological data of chromosomal aberrations of root cells caused by mercurial treatment exists. BIBLIOGRAPHIC REFERENCES: A. H. Maki and T-t. Co, "Study of Singlet-Triplet Energy Transfer in an Enzyme-Dye Complex Using Optical Detection of Magnetic Resonance." Biochemistry 15, 1229 (1976). K. P. Dinse and A. H. Maki, "Investigation of the Triplet State of DNA by Optical Detection of Magnetic Resonance Using a New Slow-Passage Technique." Chem. Phys. Letters 38, 125 (1976).